This invention relates to a device for the ejection of liquid drops.
Devices for ejection of liquid drops according to prior art comprise devices with continuous jets and devices with controlled drops. This invention is applicable only to devices with controlled drops, and they are used particularly for ink jet printer heads. They are subdivided into two main families:
devices with deformable membranes like those described in document reference [1] at the end of this description, in which ejection of a liquid drop is caused by the deformation of a membrane 11. As shown in FIG. 1, the volume of a cavity 12 delimited by this membrane 11 and filled with a liquid 13 through a pipe 14 is reduced when an actuator 10 acting on the said membrane 11 is energized. The compressibility of the liquid 13 is negligible, such that reducing the volume causes ejection of a liquid drop 15 through an opening or a xe2x80x9cnozzlexe2x80x9d 16. As described in document [2], this type of device is used particularly for biological applications. But they have many disadvantages and particularly including a deformable membrane makes the structures more fragile and frequently makes the technology complex. Furthermore, if the drops are to be ejected at high speed, the membrane deformation must be very fast, which requires an actuator with fast dynamics;
xe2x80x9cbubble-jetxe2x80x9d type devices like those described in document [3], in which ejection of a liquid drop 22 is also related to a variation of the volume of a cavity 18; but the ejection is then caused by local vaporization of the liquid. As shown in FIG. 2, the heating element 17 is placed close to the cavity 18 equipped with an opening 19 and filled with a liquid 20 supplied through a pipe 21. This type of devices is used particularly in office automation applications. But they require an increase in the temperature of the liquid medium, which can modify its characteristics and is therefore incompatible with biological applications.
The purpose of this invention is a device for ejection of liquid drops in order to overcome the disadvantages of devices according to prior art, while proposing an easy-to-make structure with very fast dynamics, and resisting high liquid pressures without increasing the temperature of the liquid.
This invention relates to a device for ejection of liquid drops comprising:
a body provided with at least one cavity filled with the said liquid and an outlet orifice for this liquid;
means of transmitting a sufficient force to the liquid to eject at least one drop; characterized in that the body is not deformable and that these means comprise means of striking a wall of the said body.
Unlike devices according to known art in which the ejection devices with simultaneous ejections provide a cavity and a striking device for each orifice, the invention can associate several orifices with a single cavity and a single striking device.
In a first embodiment, the striking means comprise a metallic mass moved by an electromagnet, the mass then moving along the centerline of the cavity output orifice.
Advantageously, the cavity may be made in a silicon substrate. For example, the cavity may be of the order of a few millimeters wide and the orifice may be of the order of 200 xcexcm wide. For other applications, the width of the same cavity may be about 60 xcexcm.
In this first embodiment, the consumable part of the device is composed of the substrate alone. With this consumable part which is easy to make, operating costs are minimized.
In one variant of this first embodiment, the cavity forms a capillary located between a microfluidic system on the upstream side and a microfluidic system on the downstream side, the mass moving in the direction perpendicular to the cavity. The diameter of the cavity is then between a few micrometers and a few hundred micrometers.
This first embodiment makes it possible to eject drops without adding a deformable membrane and without adding active elements machined on the substrate.
In a second embodiment, the striking device comprises at least one flexible arm that supports a mass and an electrostatic actuator. In one variant of this embodiment, the cavity forms a capillary located between a microfluidic system on the upstream side and a microfluidic system on the downstream side.
With this second embodiment, the device according to the invention can be miniaturized.
The device according to the invention may be different sizes, but it is particularly attractive if it is miniaturized. The objective is then to eject drops with very small volumes (less than 1 mm3). Advantageously, the device according to the invention can then be manufactured using the same technology, for example a xe2x80x9csiliconxe2x80x9d type technology.
The device according to the invention can be used in many different fields; for example for printer heads, or for biological applications with micropipettes for analysis, or liquid deposition systems or systems for deposition of chemical or biological reagents onto biochips, or for the distribution of a liquid in the form of droplets (injectors, etc.).